7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Dynamic Plasma Contraction of the Weakly Ionized
Non-Equilibrium Molecular Flow

M.N. Shneider1, M.S. Mokrov2, H. Zhong3 and Y. Ju1
1
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, USA
2
Department of Aeronautics and Astronautics, Stanford, CA, USA
3
Department of Mechanical Engineering, Stanford University, Stanford, CA, USAe-mail (speaker): m.n.shneider@gmail.com
Contraction of the gas discharge, when current contracts
from a significant volume of weakly ionized plasma intoa thin arc channel, was attracted attention of scientists formore than a century. Studies of the contraction (alsocalled constriction) mechanisms, besides carrying
interesting science, are of practical importance for many
applications, especially when contraction should be
prevented. In this talk, the problems related to the
dynamic contraction developing as a result of thethermal-ionization instability of the current channel
inside a weakly-ionized non-equilibrium quasineutral
positive column of a self-sustained glow discharges inmolecular gas flow with external circuit (Fig. 1, left) will
be considered. Transition from the uniform to contracted
state was analyzed. It was shown that such transition
experiences a hysteresis, and that the critical current of
the transition increases when the pressure (gas density)
drops[1,2] (Fig.1, right). It is important to note that in thehysteresis region, coexistence of the contracted anduniform state of the plasma in the discharge where thecurrent flows along the density gradient of the
background gas is possible.
The possibility of plasma-chemical instability in aflow of chemically reacting weakly ionized plasma wasrecently predicted and studied in low temperature plasma
flow in DC glow discharge[3], as well as in highrepetition rate nanosecond dielectric barrier discharges.
[4]
The results show that the plasma chemical instability
affects the critical current for the transition between thehomogeneous state and the contracted state originallytriggered by the plasma thermal-ionization. The plasmachemical
instability
cancouplewiththeionization-thermal instability via the endothermic andexothermic plasma-assisted combustion chemical
reactions by changing the local temperature.
Understanding the impact of chemical reaction kinetics
on plasma instability will open more new applications
for efficient ignition and material synthesis.
In addition, the problem of dynamic contraction in
the large volume of non-equilibrium weakly ionizedplasma is closely related to the problem of streamer toleader transitions in lightings and blue jets (transitions inlightning and “blue jets” (lightning-like phenomena in
the upper atmosphere).[5]References[1] M.N. Shneider, M.S. Mokrov, G.M. Milikh, Phys.
Plasmas 19, 033512 (2012)[2] M.N. Shneider, M.S. Mokrov, G.M. Milikh, Phys.
Plasmas 21, 032122 (2014)[3] H. Zhong, M.N. Shneider, M.S. Mokrov, Y. Ju, J.
Phys. D: Appl. Phys. 52, 484001 (2019)[4] H. Zhong, X. Yang, X. Mao, M.N. Shneider, I.V.
Adamovich, Y. Ju, PSST, 31, 114003 (2022)[5] G.M. Milikh, M.N. Shneider, M.S. Mokrov, J.
Geophys. Res. Space Physics, 119, (2014)

Figure 1. (Left): Contracting channel in axisymmetric cylindrical geometry (x,r) in our model. The arrow shows
the gas flow with the velocity u. (Right): The "current-voltage characteristic" of the glow discharge in air flow atthe different pressures and flow velocity u=50 m/s.2 E is the electric field in the positive column. The blue andred branches shown in the figures correspond to the uniform and contracted regimes, respectively. To the left ofthe hysteresis region, the uniform state of the discharge is stable; in the hysteresis region, the homogeneous stateis stable for relatively small perturbations, while finite perturbations of the plasma parameters exceeding certain
critical values lead to the growth of the contraction channel; to the right of the hysteresis region, any fluctuationsof the plasma parameters are unstable.